Rob Gilham, a director at WHG, said the firm would never plan to make a profit from heat supply.
“For several years we’ve kept charges far below the true cost by covering a large part of the expense ourselves,” he said.
“Customers have been paying around £200 per year on average for heating and hot water, well below expected energy costs for these types of properties.
“It was not sustainable to continue subsidising these low rates for a small number of customers.”
Mr Gilham said the increase meant customers were now paying the “full and fair” cost of the energy they use.
An average user would pay between £412 and £530 he said compared to the national average of £1,266, according to regulator Ofgem.
“We understand that some people are making careful choices about how they use energy, and we urge anyone who is struggling to contact us.
“We offer confidential money advice and one-to-one support, and no customer will ever be disadvantaged for raising a concern.”